This invention relates to a multiple speed power transmission mechanism, and more particularly, to apparatus for preventing a simultaneous engagement of both a low forward speed gear and a reverse speed idler gear.
Generally, in manually operated transmissions having four or more forward speeds and a reverse gear the reverse-low speed sliding gear is usually required to perform an additional function of completing the drive train through the second forward speed gear in order to minimize the massiveness of the overall transmission assembly. This is accomplished by providing suitable shifting means for sliding the reverse-low speed sliding gear axially in one direction to one extreme position to effect a low forward speed operation and to axially slide the sliding gear in the opposite direction to the second extreme position to effect a second forward speed operation. Whenever the sliding gear would be in a neutral position, that is, generally intermediate the two extreme positions, it would then be available for engagement by an axially shiftable reverse speed idler gear mounted on a separate shaft for completing the drive in reverse. Various devices have been developed for preventing the simultaneous engagement of the gears forming the low and intermediate forward speed drive trains with the gears forming the reverse speed drive trains. For example, a rotatable blocking segment is shown in U.S. Pat. No. 3,319,479, the segment being adapted to move into a position which prevents movement of the low and intermediate speed selector mechanism when the reverse gears are in an operative condition. Other mechanisms such as shown in U.S. Pat. No. 3,292,442, utilize two cam portions which provide interference preventing the inadvertent movement of a lever to be shifted into a second speed ratio position. The present invention relates to an interlock mechanism for preventing the simultaneous engagement of the low forward speed gear and reverse speed gear.